why do i keep getting this error "Error using + Matrix dimensions must agree" ?

Please assist:

When i try running the following i keep getting the above error:

%initial conditions
y0=[19.125;19.125;114.75;51;51;1;2;1;55;50;0.5;3.187;3.187;19.125;8.5;8.5;1;2;1;55;50;0.5;1.594;1.594;9.5625;4.25;4.25;1;2;1;55;50;0.5;1.594;1.594;9.5625;4.25;4.25;1;2;1;55;50;0.5;6.375;6.375;38.250;17;17;1;2;1;55;50;0.5];
t0=0;
tEnd=282;
h=0.0006944444;
N=ceil((tEnd-t0)/h);


%initilising solution
T=t0:h:tEnd;
Y=zeros(55,N+1);
Y(:,1)=y0;

%boundaries

for i=1:N  
    T(i+1)=T(i)+h;
    
    Y(Y<0)=0;
    y11=Y(11);
    y11(y11>8.5)=8.5;
              
   %update y
  
    yi=Y(:,i);
    a1=UASBFun(T(i), yi);
    a2=UASBFun(T(i)+0.5*h, yi+0.5*a1*h);
    a3=UASBFun(T(i)+0.5*h, yi+0.5*a2*h);
    a4=UASBFun(T(i)+    h, yi+       a3*h);
    yNew=yi+(h/6)*(a1+2*a2+2*a3+a4);
    Y(:,i+1)=yNew;
    
end
    
 %plotting
 
  yEnd=Y(:,end);

  plot(T,Y(50,:),'-r'); hold on
  plot(T,Y(51,:),'-g'); hold on
  plot(T,Y(52,:),'--r'); hold on
  plot(T,Y(53,:),'-k'); hold on
  plot(T,Y(54,:),'-b'); hold on
  plot(T,Y(55,:),'--g'); hold off
  
  xlabel('Time (days)'); ylabel('Concentration (g/m^3)');

Function:

function fval=UASBFun(~,y)
%Define  variables
Xaoba=y(1);      Xaobb=y(12);     Xaobc=y(23);   Xaobd=y(34);   Xaobe=y(45);
Xnoba=y(2);      Xnobb=y(13);     Xnobc=y(24);   Xnobd=y(35);   Xnobe=y(46);
Xamxa=y(3);      Xamxb=y(14);     Xamxc=y(25);   Xamxd=y(36);   Xamxe=y(47);
Xhana=y(4);      Xhanb=y(15);     Xhanc=y(26);   Xhand=y(37);   Xhane=y(48);
Xhaera=y(5);     Xhaerb=y(16);    Xhaerc=y(27);  Xhaerd=y(38);  Xhaere=y(49);
Xsa=y(6);          Xsb=y(17);         Xsc=y(28);       Xsd=y(39);        Xse=y(50);
Ssea=y(7);        Sseb=y(18);       Ssec=y(29);       Ssed=y(40);    Ssee=y(51);
Sno3a=y(8);      Sno3b=y(19);     Sno3c=y(30);   Sno3d=y(41);   Sno3e=y(52);
Sno2a=y(9);      Sno2b=y(20);     Sno2c=y(31);   Sno2d=y(42);   Sno2e=y(53);
Snh4a=y(10);     Snh4b=y(21);     Snh4c=y(32);   Snh4d=y(43);   Snh4e=y(54);
So2a=y(11);      So2b=y(22);      So2c=y(33);    So2d=y(44);     So2e=y(55);

The functions for each variable are long though hence i stop at this.

PLease someone assist here please.....

[Geoff Hayes]

Kosgey - which line of code is throwing the error message? I can't run the above because of errors with your UASBFun function (not sure what you are attempting there).

Anyway, the error message is telling you that you are trying to add two matrices together that have different dimensions...

[Kosgey Kip]

Geoff, pls find the code files attached, thanks in advance

Answer 1

[Walter Roberson]

yi is initialized from one column of Y, Y is initialized to 55 rows. So yi has 55 entries.

a1 is computed by calling UASBFun, passing in something that is ignored, and passing in yi. UASBFun takes in those 55 values, and computes 11 fval from it.

The code for calculating a2 tries to do yi + 0.5 * a1 * h . 0.5 and h are scalar, a1 is length 11 as noted a moment ago. yi is length 55 as noted a moment ago. So you are trying to add something length 55 together with something length 11. That is not going to work.

I do not think that your code can be fixed; I think you will have to abandon it.

[Kosgey Kip]

Thank you Roberson